Today's modern buildings, particularly residential buildings, often include many more water-using appliances than the buildings built a generation or more ago. Such appliances include ice makers, dishwashers, under-the-counter water filters and hot and cold water dispensers. Each of these appliances requires its own supply of water to operate. As a result, builders and plumbers are required to plumb an ever-increasing number of water lines to supply water to these appliances.
The most straightforward way to provide water to such appliances is to install a new water line, usually by tapping into an existing water line. Unfortunately, the time and effort required to tap into an existing water using conventional techniques can be difficult and time-consuming, and generally requires shutting off the water supply to the entire house or building at its source.
If the existing water line has a conventional two-way stop valve (commonly called a "stop") with an input line, a valve section and an output line (such as shown at 14 in the drawings), then the two-way stop can merely be replaced, with what is known as a three-way angle supply stop, which has two discharge ports rather than one. However, this method requires the additional expense of purchasing a new three-way valve, and also requires shutting off the water supply to the entire house or building.